Cannabinoids are a group of extracellular signaling molecules that are found in both plants and animals. Signals from these molecules are mediated in animals by two G-protein coupled receptors, Cannnabinoid Receptor 1 (CB1) and Cannabinoid Receptor 2 (CB2). CB1 is expressed most abundantly in the neurons of the CNS but is also present at lower concentrations in a variety of peripheral tissues and cells (Matsuda, L. A. et al. (1990) Nature 346:561-564). In contrast, CB2 is expressed predominantly, although not exclusively, in non-neural tissues, e.g. in hematopoietic cells, endothelial cells, osteoblasts, osteoclasts, the endocrine pancreas, and cancerous cell lines (Munro, S. et al. (1993) Nature 365:61-65; and as reviewed in Pacher, P. et al. (2006) Pharmacol. Rev. 58(3): 389-462). As such, CB1 is believed to be primarily responsible for mediating the psychotropic effects of cannabinoids on the body, whereas CB2 is believed to be primarily responsible for most of their non-neural effects.
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